Cell and membrane transport process will be examined in a variety of comparative preparations particularly suitable for studying regulatory mechanisms of general significance in physiology and experimental medicine. Urinary bladders from stenohaline marine teleosts will be used to characterize transport of strong electrolytes and water. Intracellular osmoregulatory mechanisms will be studied in red blood cells, muscle fiber and other tissues in elasmobranchs where/amino regulate cell volume when the extracellular fluid volume and osmolar content varies. Finally, tissue-culture and other in vitro methods will relate changes in fine structure of renal proximal tubule the onset and loss of ability to actively secrete several phenosulfonphthalein anionic dyes. Hemodynamic studies will analyze an apneic or "diving" reflex that causes total renal shut-down in rabbits. The preparation serves also as a particularly effective pharmacogenetic model for studying atropinesterase, an enzyme that degrades atropine and is determined by a gene in rabbits that is reported as autosomal and autonomous in identifiable strains.